Various contaminants may be attached onto the surface of a substrate to be processed, such as a semiconductor wafer (hereinafter, referred to as “wafer”), during the semiconductor manufacturing process using a semiconductor manufacturing apparatus. In order to remove the contaminants, a cleaning process is performed with respect to the surface of the wafer by using various chemical liquids.
The SPM liquid is a mixture of sulfuric acid and hydrogen peroxide, and used to remove the delaminated photoresist or other organic contaminant materials from the surface of the wafer. For instance, the SPM liquid is used for a single type wafer processing apparatus, which cleans a wafer by supplying a chemical liquid onto the surface of the wafer which rotates on a turntable, or a batch type wafer processing apparatus, which simultaneously cleans a plurality of wafers by immersing the wafers in a processing bath filled with the chemical liquid.
In the batch type wafer processing apparatus, tens of wafers are immersed in the processing bath filled with the SPM liquid heated at the temperature of about 100° C. to 130° C., and the wafers are taken out of the processing bath after a predetermined time has elapsed. Then, next tens of wafers are immersed in the processing bath, so the wafers can be continuously processed. As the wafers are being continuously processed, the SPM liquid filled in the processing bath may stick onto the surface of the wafers and some SPM liquid may be discharged out of the processing bath, so that the liquid level of the SPM liquid may be lowered. Thus, the sulfuric acid or the hydrogen peroxide is periodically supplemented to the SPM liquid.
However, since the hydrogen peroxide is a relatively unstable material and gradually decomposed to create water, the concentration of the sulfuric acid in the SPM liquid is slightly lowered even if the sulfuric acid or the hydrogen peroxide is supplemented to compensate for the lowered level of the SPM liquid. If the concentration of the sulfuric acid is lowered, the function for removing the contaminant material is degraded, so that the wafer processing in the processing bath may be periodically stopped to exchange the SPM liquid with a new SPM liquid. For this reason, the wafer processing efficiency may be lowered and consumption of the SPM liquid may be increased, so that the cost for the chemical liquids may rise.
Regarding the supplement of the sulfuric acid or the hydrogen peroxide into the SPM liquid, for example, Japanese Unexamined Patent Publication No. 2000-164550 (paragraphs 0021, 0031-0033 and 0071, and FIG. 3) discloses a technology in which a concentration detection unit is provided in a processing bath to detect the concentration of the sulfuric acid in the processing bath to supplement the sulfuric acid such that the concentration of the sulfuric acid in the SPM liquid may not be lowered below the predetermined level. According to the technology disclosed in Japanese Unexamined Patent Publication No. 2000-164550, a greater amount of sulfuric acid may be supplemented in order to compensate for the lowered concentration of the sulfuric acid caused by the decomposition of the hydrogen peroxide, and the frequency of the exchange for the SPM liquid due to the lowered concentration of the sulfuric acid is reduced, so that the total amount of use for the sulfuric acid can be reduced.
In addition, Japanese Unexamined Patent Publication No. 9-8034 (paragraph, 0008) discloses a technology in which the SPM liquid (referred to as sulfuric acid hydrogen peroxide) is heated at the temperature of about 120□□140□ to remove a resist layer from the surface of a wafer. However, the technology disclosed in Japanese Unexamined Patent Publication No. 9-8034 fails to disclose the solution for solving the problems derived from the lowering of the concentration of the sulfuric acid and the exchange of the entire SPM liquid caused by the lowering of the concentration of the sulfuric acid.
The technologies disclosed in the above patent documents require the detection unit for detecting the concentration of the sulfuric acid, so the cost for the apparatus may rise. In addition, since the level of the chemical liquids in the processing bath cannot be controlled by the supplement of the chemical liquids to control the concentration of the sulfuric acid, there is a case that supplements an excessive amount of the sulfuric acid beyond the critical level of the concentration to maintain the level of the SPM liquid in the processing bath even if the concentration of the sulfuric acid is sufficient, so the consumption of the sulfuric acid may not be sufficiently reduced.